Thanks RB, you're right, I can just mem:write_i8(0xc0c1,data).

I don't know why I couldn't get it to work before, probably because I had an OBOE where I write the registers.

I had a for loop whose index started at 1 but the register write was mem:write_i8(0xc0c1,128+i) instead of write_i8(0xc0c1,128+(i-1)) so the wrong register was getting the value.


Code
cpu = manager:machine().devices[":maincpu"];mem = cpu.spaces["program"]

reginitarray = {2,196,14,255,3,118,3,15}

for i=1,table.maxn(reginitarray) do 
dummy=mem:read_i8(0xc0c1);
mem:write_i8(0xc0c1,reginitarray[i]); mem:write_i8(0xc0c1,128+(i-1)); end

Code
-- dofile("tms9918_apple_memspace.lua")

fontarray = {32, 0,0,0,0,0,0,0,0,
33, 24,60,60,24,24,0,24,0,
34, 108,108,0,0,0,0,0,0,
35, 108,108,254,108,254,108,108,0,
36, 24,62,96,60,6,124,24,0,
37, 0,198,204,24,48,102,198,0,
38, 56,108,104,118,220,204,118,0,
39, 24,24,48,0,0,0,0,0,
40, 12,24,48,48,48,24,12,0,
41, 48,24,12,12,12,24,48,0,
42, 0,102,60,255,60,102,0,0,
43, 0,24,24,126,24,24,0,0,
44, 0,0,0,0,0,24,24,48,
45, 0,0,0,126,0,0,0,0,
46, 0,0,0,0,0,24,24,0,
47, 3,6,12,24,48,96,192,0,
48, 60,102,110,126,118,102,60,0,
49, 24,56,24,24,24,24,126,0,
50, 60,102,6,28,48,102,126,0,
51, 60,102,6,28,6,102,60,0,
52, 28,60,108,204,254,12,30,0,
53, 126,96,124,6,6,102,60,0,
54, 28,48,96,124,102,102,60,0,
55, 126,102,6,12,24,24,24,0,
56, 60,102,102,60,102,102,60,0,
57, 60,102,102,62,6,12,56,0,
58, 0,24,24,0,0,24,24,0,
59, 0,24,24,0,0,24,24,48,
60, 12,24,48,96,48,24,12,0,
61, 0,0,126,0,0,126,0,0,
62, 48,24,12,6,12,24,48,0,
63, 60,102,6,12,24,0,24,0,
64, 124,198,222,222,222,192,120,0,
65, 24,60,60,102,126,195,195,0,
66, 252,102,102,124,102,102,252,0,
67, 60,102,192,192,192,102,60,0,
68, 248,108,102,102,102,108,248,0,
69, 254,102,96,120,96,102,254,0,
70, 254,102,96,120,96,96,240,0,
71, 60,102,192,206,198,102,62,0,
72, 102,102,102,126,102,102,102,0,
73, 126,24,24,24,24,24,126,0,
74, 14,6,6,6,102,102,60,0,
75, 230,102,108,120,108,102,230,0,
76, 240,96,96,96,98,102,254,0,
77, 130,198,238,254,214,198,198,0,
78, 198,230,246,222,206,198,198,0,
79, 56,108,198,198,198,108,56,0,
80, 252,102,102,124,96,96,240,0,
81, 56,108,198,198,198,108,60,6,
82, 252,102,102,124,108,102,227,0,
83, 60,102,112,56,14,102,60,0,
84, 126,90,24,24,24,24,60,0,
85, 102,102,102,102,102,102,62,0,
86, 195,195,102,102,60,60,24,0,
87, 198,198,198,214,254,238,198,0,
88, 195,102,60,24,60,102,195,0,
89, 195,195,102,60,24,24,60,0,
90, 254,198,140,24,50,102,254,0,
91, 60,48,48,48,48,48,60,0,
92, 192,96,48,24,12,6,3,0,
93, 60,12,12,12,12,12,60,0,
94, 16,56,108,198,0,0,0,0,
95, 0,0,0,0,0,0,0,254,
96, 24,24,12,0,0,0,0,0,
97, 0,0,60,6,30,102,59,0,
98, 224,96,108,118,102,102,60,0,
99, 0,0,60,102,96,102,60,0,
100, 14,6,54,110,102,102,59,0,
101, 0,0,60,102,126,96,60,0,
102, 28,54,48,120,48,48,120,0,
103, 0,0,59,102,102,60,198,124,
104, 224,96,108,118,102,102,230,0,
105, 24,0,56,24,24,24,60,0,
106, 6,0,6,6,6,6,102,60,
107, 224,96,102,108,120,108,230,0,
108, 56,24,24,24,24,24,60,0,
109, 0,0,102,119,107,99,99,0,
110, 0,0,124,102,102,102,102,0,
111, 0,0,60,102,102,102,60,0,
112, 0,0,220,102,102,124,96,240,
113, 0,0,61,102,102,62,6,7,
114, 0,0,236,118,102,96,240,0,
115, 0,0,62,96,60,6,124,0,
116, 16,48,124,48,48,52,24,0,
117, 0,0,204,204,204,204,118,0,
118, 0,0,204,204,204,120,48,0,
119, 0,0,198,214,214,108,108,0,
120, 0,0,99,54,28,54,99,0,
121, 0,0,102,102,102,60,24,112,
122, 0,0,126,76,24,50,126,0,
123, 14,24,24,112,24,24,14,0,
124, 24,24,24,24,24,24,24,0,
125, 112,24,24,14,24,24,112,0,
126, 114,156,0,0,0,0,0,0,
127, 0,0,0,0,0,0,0,0
}

cpu = manager:machine().devices[":maincpu"];mem = cpu.spaces["program"]

reginitarray = {2,196,14,255,3,118,3,15}

for i=1,table.maxn(reginitarray) do 
dummy=mem:read_i8(0xc0c1);
mem:write_i8(0xc0c1,reginitarray[i]); mem:write_i8(0xc0c1,128+(i-1)); end

-- name table at 0x3800

mem:write_i8(0xc0c1,0x0);
mem:write_i8(0xc0c1,0x38+64);

for j=0,2 do
for i=0,255 do mem:write_i8(0xc0c0,i) end
end

-- color table at 0x2000

mem:write_i8(0xc0c1,0x0);
mem:write_i8(0xc0c1,0x20+64);

for i=0,6143 do mem:write_i8(0xc0c0,15*16+4) end


-- pattern table at 0, but we'll start at 0x100 because our character data starts at 32

mem:write_i8(0xc0c1,0x0);
mem:write_i8(0xc0c1,0x0+1+64);  -- going to write data, so we add 64

i=1
while(true) do
 if i>table.maxn(fontarray) then break; end;
  charnum = fontarray[i];
  i = i + 1;
  for j=1,8 do  mem:write_i8(0xc0c0,fontarray[i]); i = i + 1; end
end

a = "Writing to the TMS9918 using addresses C0C0 and C0C1 with Lua"

xpos = 0  -- horizontal character pos (in characters)
ypos = 16*8  -- y character pos (in pixels)

copychar = {}  -- init array copychar

for aindex = 1,string.len(a) do

screenaddr = math.floor(ypos/8)*256+xpos*8 + (ypos % 8)

char = string.byte(a,aindex)
charaddr = char*8

-- get char into copychar array
mem:write_i8(0xc0c1,charaddr % 256);
mem:write_i8(0xc0c1,math.floor(charaddr/256));  -- going to read data, don't need to add anything

for i = 0,7 do copychar[i]=mem:read_i8(0xc0c0) end
mem:write_i8(0xc0c1,screenaddr % 256);
mem:write_i8(0xc0c1,math.floor(screenaddr/256)+64);  -- going to write data, add 64

for i= 0,7 do mem:write_i8(0xc0c0,copychar[i]); end
xpos = xpos + 1
end